Method of and apparatus for vacuum sealing packs

ABSTRACT

This invention relates to a method of and apparatus for vacuum sealing packs. Primarily, there is provided a cover movable in a first direction from a position adjacent a first sealing station to a position adjacent a second sealing station, and then in a second direction substantially perpendicular to the first direction to form a closed vacuum sealing chamber at the second station whereat a vacuum sealing operation is conducted. Preferably an electromagnetic arrangement is provided so that the cover can be precisely positioned adjacent the sealing station at the end of movement in the first direction.

United States Patent 2.601,020 6/1952 Hopp Inventor Alain Gerard Saint-Coud, France Appl. No. 868.065 Filed Oct. 21, I969 Patented Aug. 10, I971 Assignee W. R. Grace 8: Co.

' New York, N.Y.

METHOD OF AND APPARATUS FOR VACUUM SEALING PACKS 9 Claims, 5 Drawing Figs.

U.S.C| .l

53/85,53/86, 53/l l2 B Int.Cl.....; B65b 31/02 FieldoISearch 53/86, 84, 85,79,93,ll2B

References Cited UNITED STATES PATENTS 2,778,177 l/l957 Mahaffyetal 53/86 2,833,096 5/1958 Randall 53/86 Primary Examiner-Travis S. McGehee Attorneys-J0hn J. Toney. William D. Lee, Jr. and Edward J.

Hanson, Jr.

' lar to the first direction to form a closed vacuum sealing chamber at the second station whereat a vacuum sealing operation is conducted. Preferably an electromagnetic arrangement is provided so that the cover can be precisely positioned adjacent the sealing station at the end of movement in the first direction.

Patented Aug. 10, 1971 3,597,897

4 Sheets-Sheet 1 Invenlor ALAIN GERARD B 1mm...

A Horn Pmm'nftetl Aug, 10, 1971 4 Sheets-Sheet 2 inventor ALAIN GERARD 8mm 9.. J1

Atlorn y Patented Aug. 10, 1971 4 Shoots-Sheet Z5 Inventor ALAIN GERARD QMM D.

A ttorn Patented Aug. 10, 1971 4 Sheets-Sheet 4 Invenlor ALAIN GERARD v tmWfl74 A Horn METIIOI) OF AND APPARATUS FOR VACUUM SEALING PACKS THIS INVENTION relates to a method of, and apparatus for vacuum-sealing packs.

Machines are known for vacuum-sealing packs. These machines generally comprise on a fixed plate two stations which are each provided with a supporting element, a port connected to a vacuum pump, and a sealing device the mobile portion of which cooperates with a pressing jaw. These machinesalso comprise a single mobile cover intended to cover one station and now the other, to isolate it from the exterior whilst a relative vacuum is established therein and the sealing of the pack is carried out.

The aforesaid cover is connected to the fixed plate in such a manner as to be manually displace'able from one station to the other without touching, the packed products arranged on the said stations. For this purpose, the connection of the cover with the plate is effected at each side by means of two pivoting links which are parallel to one another and ofequal length. By

means of this device, a circular translational movement of the cover is obtained which permits the cover, in moving parallel to itself, to be raised so as not to encounter the packed goods.

A first disadvantage of this type of machine resides in the fact that the lateral walls of the cover have to be inclined considerably, especially if the packed goods are relatively high, if

one wishes to avoid the covers striking the said goods during the circular translational movement. As a result, the internal volume of the cover is'larger than would besufficient for it simply to cover the product; consequently a considerable amount of energy has to be used in order to provide a vacuum and more especially the vacuum-establishing operation takes longer.

Furthermore, the pivoting movement of the cover-carrying link is difficult to start manually since it is conducive to lifting the said cover; The operator is needlessly fatigued as a result. Also it is not possible to reduce the fatigue since in order to reduce the inclination of the lateral walls of the cover and the general bulk of the machine, it is necessary to choose links of limited length.

The known machines are arranged so that in their operating cycle, the operations of onloading and off-loading the products are carried out manually or automatically. But, in the latter case, automatic conveyors are used which comprise independent parts which constitute the supporting elements situated at the two machine stations. These automatic devices are expensive and they consume energy, and their control in relation to time with that of the other operations requires excessive complication of the machine and a loss of time at high working rates.

Furthermore, the control of the sealing devices used in these known machinesis triggered by a time switch, that is to say with a certain amount of delay relatively to the instant comprising a plurality of sealing stations each being provided with vacuum-applying means and a cover movable between the sealing stations to, provide a closed vacuum-sealing chamber sequentially at each station, the cover being mounted for movementin a first direction between a position adjacent onesealingstation and a position adjacent a second sealing station and in a second direction substantially perpendicular to the said first direction to form the closed vacuum chamber at the respective sealing stations.

Preferably, the apparatus includes a temporary linking and coupling device associated with each sealing station for positioning the cover in a precisely defined position adjacent each direction.

Each temporary linking and coupling device may include a relatively fixed linking and coupling'member, which in the linked and coupled position of the cover supplies electrical power to electrical units carried by the cover member.

Further, each temporary linking and coupling device may comprise a first transformer half circuit including a primary winding mounted on the fixed member and a second transformer half circuit including a secondary winding mounted on the cover member, the cover and the fixed member being so arranged that the first and second half circuits engage and are held in linked engagement by induced magnetic flux in the precisely defined position.

According to a further aspect of the present invention there is provided a method of vacuum-sealing packs comprising moving a cover member from a position adjacent a first sealing station in a first direction to a position adjacent a second sealing station and then moving the cover member in a second direction substantially perpendicular to the first direction to form a closed vacuum-sealing chamber at the second sealing station and vacuum sealing a pack positioned at the second sealing station. I

An illustrative embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is-a simplified perspective view of one form of apparatus;

FIG. 2 shows a vertical sectional view taken on a larger scale of the line Il-II of FIG. 1 and shows more particularly the device for actuating in the ascending and descending sense the mobile assembly in which the cover is integrated.

FIGS. 3 and 4 are simplified sectional view taken on a larger scale on the lines III-III and IV-IV respectively of FIG. 1 illustrating the pressing jaw accommodated in the cover and the device for causing inclination of each supporting element, and

FIG. 5 is a pneumatic and electrical diagram showing the control of the various parts of the apparatus.

Referring now to FIG. 1 there is shown apparatus comprising arigid frame 1 having a plate 2 mounted thereon. On the top plate 2 there are provided two working stations 3 and 4 each of which is adapted to be covered selectively by a mobile cover 5 to form a closed chamber in which a motor-pump assembly 6 can establish a sufficient vacuum for vacuum-sealing.

Provided at each of the stations 3 and 4 (FIGS. 1 and 3) is a fixed insulating bar 7 on which are mounted a heating strip 8 for the sealing of the packs and a cutting wire 9 for cutting-off excess packaging material, this strip and wire are connected to an electrical current source.

At each of the stations 3 and 4 there is also provided a sup porting element generally indicated by the reference numeral 10 and constituted by an inclinable roller table. In the example illustrated in FIGS. 1 and 4, this table comprises two flat bars 11 connected to one another by parallel rods 12 on which wheels or sleeves 13 are freely mounted. This table is simply positioned on the plate 2 and is articulated at one side of the apparatus about fixed shafts 14 extending through the ends of the bars 11, and through brackets 15 fixed to the plate 2. Consequently, when the table 10 is lifted at its unsecured end it will pivot about the shafts l4 and is inclined so that it presents a descending slope from the front towards the rear of the apparatus. Consequently, packed goods that have been vacuum sealed in the apparatus can be transported to a discharge table 16 by merely pivotingthe table 10 upwardly. The table 16 is mounted rearwardly of the plate 2 by butterfly nuts 17, which are adjustable so that the inclination of the table 16 may be regulated. In practice a discharge conveyor cooperates with the table 16 thus enabling sealed packs to be transported away from the apparatus.

The cover 5 is guided along a horizontal slideway which comprises (FIG. 1 and 2), two parallel cylindrical bars 18, which are rigidly connected at their free ends to angled cross members 19 and 20. The bars 18 are located above the cover and extend through apertures in projecting portions 21 of the cover 5. Conveniently these apertures are provided with bushings, ball bearing sleeves or other guide elements, thus.

enabling the cover to be easily displaced manually in a horizontal direction by means of a handle 22.

The assembly constituted by the horizontal slideway and the cover 5 is movable vertically relative to the frame 1. For this purpose, the cross member 19 is secured to two columns 23 extending through a boss 24 of the plate 2, the boss 24 is provided with guide elements such as bushings, or ball bearing sleeves. In a similar manner, the crossmernber is secured with column 25 extending through a boss 26 in a similar manner to the columns 23. All these columns project within the frame 1 and are connected to one another rigidly at a sufficiently low level, in order to constitute with the horizontal slideway and the cover a vertically mobile assembly. For example, the columns 25 are connected by a lower crossmernber 27 and the columns 23 by another lower crossmernber these two crossmembers 27 being themselves connected by a connecting bar 28 extending parallel to the horizontal slideway 18.

The mobile assembly thus constituted is adapted to be displaced vertically by an actuating device generally indicated by the numeral 29 and which may be of any desired type. However, in the example illustrated in FIG. 2, the device 29 comprises a jack 30 interposed between the fixed portion of the frame 1 and the central portion of the bar 28 of the mobile assembly. However, since the apparatus comprises a motorpump arrangement 6 the jack 30 is conveniently of a vacuum type. Furthermore, the jack is preferably the single-acting type and controls the upward movement of the mobile assembly, while the downward movement can be effected automatically by gravitational force. The cylinder 31 of the jack 30 can then be fixed on the bar 28 and the piston rod 32 articulated below the plate 2. In this case, the upper connecting pipe 33 of the jack cylinder is connected permanently to the atmosphere whereas its lower connecting pipe 34 is adapted to be connected by means described hereinafter either to the vacuum generator 6 or to the atmosphere.

The actuating device 29 can be constituted solely by the jack 30 which, under these conditions, is of a relatively large diameter in order to develop a force at least equal to the total weight of the mobile assembly. However a smaller jack may be employed if a counterpoise arrangement is provided for the mobile assembly. Such a counterpoise device, may, for instance, comprise a spring 35 interposed between a fixed portion of the frame 1 and the mobile assembly. However, since the preload of the spring will vary in accordance with its elongation, the load on the jack 30 will not be constant. In order to remedy this, a correcting cam 36 is provided.

In the example illustrated in H0. 2, the cam 36 and a sprocket 37 are mounted on a shaft 38 mounted freely in a bearing 39 and fitted below the plate 2. A chain 40 is attached by its lower end to a central member 41 of the bar 28. This chain 40 is in part wound over the sprocket 37 and is fixed thereto by its upper end link. Another chain 42 applied to the correcting profile of the cam 36 is fixed at one of its ends to the cam and attached at its other end to the spring 35. The spring 35 is a tension spring and is attached at its free end to a support 43 mounted on the frame 1. The spring 35 tends to lift the mobile assembly byapplying thereto, through the agency of the chain 40, a force which is directed upwards and is substantially constant, by means of the action of the profile of the cam 36. In practice this force is less than the weight of the assembly, which has the result of relieving the action of the jack 30.

it will be seen from the foregoing that by subjecting the jack 30 to negative pressure the upward movement of the mobile assembly and, more particularly, the cover 5, is achieved. This upward movement is strictly vertical since the coupling means described hereinafter are provided between the cover and the crossmernber 19 or the crossmernber 20. Consequently, the

vacuum-packed products located on the table 10 at the station 4 are not damaged by the cover during its upward movement. When cover 5 is in the upper position after completing a sealing operation at the station 4, all the operator has to do is to displace the cover manually along the guide bars 18 to bring it above the station 3 and couple it to the crossmernber 19. By connecting the jack 30 tothe atmosphere, the mobile assembly will descend by gravitational force over a pack to be sealed without damaging the pack.

The two bars 7 for sealing and cutting at the stations 3 and 4 cooperate with a single jaw 44 (FIG. 3) accommodated in the cover 5. This jaw is vertically movable in the cover by means ofajack arrangement.

In the example illustrated in FIG. 3, the actuation and, if appropriate, the guiding of the jaw 44 are effected by means ofa jack in the form of a tubular envelope 45 made of elastic material which is carried by the cover and connected to the jaw. This envelope is adapted to be connected either to the chamber within the cover or to the atmosphere by an element described hereinafter. If the pressures prevailing in the envelope 45 and in the cover 5 are balanced, either by ambient pressure or the lower pressure produced by the vacuum pump, the envelope is in a position of rest (FIG. 3) wherein the jaw 44 is spaced from the electrodes 8 and 9, even if the cover 5 is applied against plate 2. On the other hand, if the pressure prevailing in the envelope 45 is the ambient atmospheric pressure and the cover is subjected to vacuum, the envelope is inflated and applies the jaw 44 with sufficient force against the electrodes 8 and 9, pressing the two walls of a pack arranged between them. Of course, it does not matter much whether the pack in question is a bag containing a bulky product such as an entire ham, or whether it is a small packet containing a product which is not very bulky, such as slices of ham.

ln order to control the jack 30 and hence the upward or downward movement of the cover 5, the control of the element which regulates the connection to the motor-pump arrangement 6 of the station to be subjected to vacuum (which is selected by the cover 5) and the control of the element which controls the connection of the envelope 45 carried by the cover, either to the latter or to the atmosphere, various means may be used and, for example, an electrical or pneumatic program control device which trips the aforesaid controls in timed manner.

A preferred form of control device is shown very diagrammatically in FIG. 5.

Referring now to FIG. 5 there is shown a control device comprising two three-way electromagnetic valves 46 and 47, connected respectively by a conduit 48 to the vacuum pump of the arrangement 6, to the atmosphere by connecting pipe 49 or 50 and to a port 51 or 52 provided in the plate 2 at the location of the station 3 or 4 respectively. In the condition of rest, that is to say when control windings 53 and 54 of the electromagnetic valves 46 and 47 are not energized, these electromagnetic valves connect the ports 51 and 52 to the connecting pipes 49 and 50 connected with the atmosphere. On the other hand, when the winding 53 or 54 is energized, the corresponding electromagnetic valve 46 or 47 connects the port 51 or 52 to the vacuum pump of the arrangement 6. A microcontact 55 is mounted on the crossmernber l9 opposite a pushbutton 56 carried by the cover 5. This microcontact, by means ofa branch line 57 of the main electrical line 58 supplying the motor of the arrangement 6, controls the energization of the winding of a relay 59 whose contact itself controls the connection of the control winding 53 of the electromagnetic valve 56 to a branch 60 of the line 58. In a similar manner a microcontact 61 is mounted on the crossmernber 20 opposite a control push member 62 carried by the cover 5. This microcontact is connected to a branch 63 of the line 58 provided for the energization of the winding of a relay 64 whose contact is connected to another branch 65 of the line, supplying the control winding 54 of the electromagnetic valve 47.

The control device shown in FIG. 5 further includes another three-way electromagnetic valve 66 which is connected by a conduit 67 tothe vacuum pump of the arrangement 6, to the atmosphere by a connecting pipe 68'and by a conduit 69 to the lower connecting pipe 34 of the jack 30 for actuating the mobile assembly 5-19-20. As in theiprevious case, the control winding 70 of the electromagnetic valve 66 is connected in series to a branch 71 of the line 58 and under the control of a relay 72. The energizationwinding of this relay is itself connected in series to another branch 73 of the line and under the control of either a microcontact 74 carried by' the crossmember 20 or a microcontact 75 carried by the crossmember 19. For this purpose, these microcontacts 74 and 75, which are also controlled by push members 76 and 77 of the cover 5, are connected by means of conductors 78 in parallel to one another and in series to the branch 73.

The electromagnetic valves 46, 47 and 66 are fixed and accommodated in the frame 1. The device shown in FIG. 5 comprises another three-way electromagnetic valve 79 which is mounted in the cover 5: The electromagnetic valve 79 opens through a connecting pipe 80 into the cover, is connected through a connecting pipe 81 to the inflatable envelope 45 acting on the pressing jaw 44, and is connected to the atmosphere by a conduit 82. To control the electromagnetic valve 79 use is preferably, but not necessarily, made of two devices for temporarily connecting the mobile assembly to a coupling element at both of the stations 3 and 4 for positioning the cover in position and for supplying electrical energy to elements arranged in the cover. In practice these two devices permit not only the controlling of the electromagnetic valve 79 (and, where appropriate, supplying other electrical comwinding 85 mounted on the'magnetic half-circuit 83 is connectedto a branch 86 of the line 58 and under the electrical control of an element sensitive to the pressure prevailing in the cover 5. In the example illustrated, this element is a contact manometer 87 whose pneumatic chamber is connected by a conduit 88 to a pressure pickup 89 situated at the station 3 of the apparatus. The contact of this manometer is connected in series to the branch 86 and it openslwhen the pressure prevailing in the cover 5 covering the station 3 corresponds to the vacuum rate selected for sealing. The secondary winding 90 mounted on the magnetic half-circuit 84 of the cover is connected by conductors 91 to the terminals of the energization winding 92 of the electromagnetic valve 79.

In a similar manner, the second device comprises a magnetic halfscircuit 93 mounted on the cover 5 and whose secondary winding 94 is connected by conductors 95 to the terminals of the energization winding 92 of the electromagnetic valve 79. This device also comprises another magnetic halfcircuit 96 mounted on the crossmember 2t) and whose primary winding 97 is connected to a branch 98 of the line 58 and under the control of a contact manometer 99 whose pneumatic chamber is connected by a conduit 100 to a pressure pickup 101 situated at the station 4 of the machine.

In use,-the above described apparatus, operates as follows.

When the mobile assembly is situated in its upper position, the

ing closes across the complete magnetic circuit and the forces which appear tend to hold the two parts 93 and 96 secured to one another. Furthermore, the magnetic field gives rise by induction in the secondary winding 94 to an electrical current An'la which supplies the winding 92 controlling the electromagnetic valve 79. As a result, the mobile part of the electromagnetic valve connects the envelope 45 of the jaw 44 to the connecting pipe projecting into the cover 5 and, since the pressures prevailing in the latter and in the envelope tend to balance, the jaw 44 will remain spaced from the electrodes 8 and 9 even when the cover 5 is applied to the plate 2.

In the aforesaid position and at the instant when the cover 5 comes to abut on the crossmember 20, the two microcontacts 61 and 74 are closed by the push members 62 and 76.

The microcontact 61 detects which station the cover 5 has arrived at, and closes the supply circuit 63 of the relay 64 which immediately, or with a slight delay, connects to its own supply circuit 65 the control winding 54 of the electromagnetic valve 47. The mobile part of the latter then connects the pipe 68 so that the jack 30 is connected to the atmosphere by its lower connecting pipe 34. Under these conditions, the mobile assembly and more particularly the cover 5 descend by gravitational force until the latter is in sealing-tight contact with the plate 2.

Vacuum is then established progressively in the cover 5 and in the pack or packs containing the product or products to be sealed. The vacuum is also established in the envelope 45. When the pressure in the cover 5 reaches the value selected for sealing, the contact of the manometer 99 opens and the result is that the primary winding 97 of the transformer is no longer supplied. The secondary winding 94 can then no longer supply the energization winding 92 of the electromagnetic valve 79. The latter returns to its original position and consequently it connects the envelope 45 to the atmosphere. The envelope 45 is then inflated and applies the jaw 44 to the electrodes 8 and 9 through the walls of the pack or packs. The pressure exerted is substantially equal to the difference between the atmospheric pressure and a reduced pressure prevailing in the cover. Since the electrodes'8 and 9 are supplied, the weldingof the walls of thepack is effected together with the cutting of the excess material from the packs.

Then the supply to the control winding 70 of the electromagnetic valve 66 is interrupted. This operation can be carried out bythe relay 72 if the latter is of the type having a delayed-action cutoff. It may also be effected by a manometer 99 if the latter comprises a second contact with delayed action connected in series with the branch 71. In any case, as soon as the winding 70 is no longer supplied, the electromagnetic valve 66 connects the conduits 67 and 69 to one another, that is to say the vacuum pump of the set 6 to the actuating chamber of the jack 30.

At the same time, the supply to the control winding 54 of the electromagnetic valve 47 is itself interrupted. This operation can be carried out in the same manner as previously, that is to say by using a relay 64 of the type with delayed-action cutoff or a third delayed-action contact of the manometer 99. In any case, as soon as the winding 54 is no longer supplied, the electromagnetic valve 47 connects the port 52 to the connecting pipe 50 and thus connects to the atmosphere the internal chamber in the cover 5 and the envelope 45.

Thus with the pressures being balanced, the jaw 44 moves upwards and frees the pack. Furthermore, as the cover 5 is connected to the atmosphere while the jack 30 is under vacuum, the mobile assembly moves upwards in its entirety. The cover 5 is then positioned above the sealed product or products and can therefore be displaced by an operator as far as the crossmember 19, a position in which it is situated vertically above the station 3.

The same cycle as that described hereinbefore takes place but this time using the transformer 83-84, the microcontacts 55 and 75, the electromagnetic valve 46 and the contact manometer 87 as well as the electromagnetic valves 79 and 66 as previously,

Furthermore, during the upward movement of the mobile assembly the cover causes the table 10 of the station 4 to pivot about the shaft 14. The covers 5 frees the table when the inclination reached is sufficient to allow the sealed products to descend by gravitational force towards the rear table 16 to be discharged; being freed, the table 10 returns of its own accord to the horizontal position to await further products to be sealed.

To effect this temporary fixing of the cover to the table, any suitable mechanical, pneumatic or electrical arrangements may be used.

ln the form of embodiment illustrated in the drawings, the fixing device is of a mechanical type and may be provided either at only one side of the table 10 or at both. This device comprises as shown in H6. 4, two attaching elements 102 and 103 provided respectively on the cover 5 and the table 10, one of these elements being withdrawable. For example, the element 102 is a tooth fast with the cover 5 and projecting within the cover, whereas the element 103 is a lever mounted to be pivotable about a shaft 104 of the table 10, connected to a spring 105 bearing on the latter and provided at the end with a tooth 106. Whilst the cover 5 descends, its fixed tooth 102 slightly withdraws the mobile tooth 106 which, under the action of the spring 105, takes this tooth 102 as soon as the cover has arrived at the lower position. Consequently, the cover 5 can entrain in its upward movement the lower portion of the table 10 and thus cause it to pivot, When this table reaches the position of maximum inclination shown in broken lines, the tooth 106 is released since the lever 103 provided with the tooth is fast with an extension 107 bearing on a guide ramp 108 of the plate 2, a ramp which, at a specific level, causes the pivoting of the lever in opposition to the action of the spring 105.

Such an arrangement can be modified, for instance, by utilizing an electromagnet arranged in the cover and acting on a push member situated opposite a catch provided in the table 10. It then suffices to control the supply of this electromagnet by means of suitably arranged microcontacts.

lclaim:

1. Apparatus for vacuum-sealing packs, such apparatus comprising:

a. a plurality of sealing stations;

b. a plurality of vacuum-applying means, one of said vacuum-applying means being provided at each sealing station;

0. cover means, said cover means being movable between the sealing stations to provide a closed vacuum sealing chamber sequentially at each station;

d. first means for positioning the cover means in a first direction above one sealing station; and

e. second means for moving the cover means in a second direction substantially perpendicular to the said first direction to form a closed vacuum-sealing chamber at the respective sealing stations.

2. Apparatus according to claim 1 in which the said first means includes a guide arrangement for guiding the cover in the said first direction.

3. Apparatus according to claim 1 in which the said second means includes a jack arrangement for moving the cover means in the said second direction.

4. Apparatus according to claim 3 in which the said second means includes a counterbalance device, said counterbalance device being adapted to cooperate with the jack arrangement during movement of the cover means in the said second direction.

5. Apparatus according to claim 1 wherein said first means includes a plurality devices for temporary linking and coupling, one of said temporary linking and coupling devices being associated with each sealing station for positioning the cover means in a precisely defined position above each sealing station at the end of its movement in the said first direction.

6. Apparatus according to claim 5 in WhlCh each temporary linking and coupling device includes a fixed linking and coupling member, which in a linked and coupled position of the cover member apply electrical power to electricalunits carried by the cover member.

7. Apparatus according to claim 5 in which each temporary linking and coupling device comprises a stationary member, a first transformer half-circuit including a primary winding, said first transformer half-circuit being mounted on the fixed member and a second transformer half-circuit including a secondary winding, said second transformer half-circuit being mounted on the cover means, the cover means and the fixed member being so arranged that the first and second half-circuits are held engaged and linked by induced magnetic flux in said precisely defined position.

8. Apparatus according to claim 1 including sealing members at each sealing station and in which the cover means has a positioning device for bringing the portion of a pack to be sealed, positioned at a sealing station, into engagement with the sealing members of the sealing station to allow sealing to take place.

9. Apparatus according to claim 8, in which the positioning device includes a member for engaging the pack, an expandable envelope for moving the member toward and away from the sealing members of the sealing station in dependence of the relationship of the pressure in the envelope and the pressure in the sealing station, and a three-way valve, said threeway valve connecting the interior of the envelope with either the atmosphere or the interior of the cover during movement in the first direction. 

1. Apparatus for vacuum-sealing packs, such apparatus comprising: a. a plurality of sealing stations; b. a plurality of vacuum-applying means, one of said vacuumapplying means being provided at each sealing station; c. cover means, said cover means being movable between the sealing stations to provide a closed vacuum sealing chamber sequentially at each station; d. first means for positioning the cover means in a first direction above one sealing station; and e. second means for moving the cover means in a second direction substantially perpendicular to the said first direction to form a closed vacuum-sealing chamber at the respective sealing stations.
 2. Apparatus according to claim 1 in which the said first means includes a guide arrangement for guiding the cover in the said first direction.
 3. Apparatus according to claim 1 in which the said second means includes a jack arrangement for moving the cover means in the said second direction.
 4. Apparatus according to claim 3 in which the said second means includes a counterbalance device, said counterbalance device being adapted to cooperate with the jack arrangement during movement of the cover means in the said second direction.
 5. Apparatus according to claim 1 wherein said first means includes a plurality devices for temporary linking and coupling, one of said temporary linking and coupling devices being associated with each sealing station for positioning the cover means in a precisely defined position above each sealing station at the end of its movement in the said first direction.
 6. Apparatus according to claim 5 in which each temporary linking and coupling device includes a fixed linking and coupling member, which in a linked and coupled position of the cover member apply electrical power to electrical units carried by the cover member.
 7. Apparatus according to claim 5 in which each temporary linking and coupling device comprises a stationary member, a first transformer half-circuit including a primary winding, said first transformer half-circuit being mounted on the fixed member and a second transformer half-circuit including a secondary winding, said second transformer half-circuit being mounted on the cover means, the cover means and the fixed member being so arranged that the first and second half-circuits are held engaged and linked by induced magnetic flux in said precisely defined position.
 8. Apparatus according to claim 1 including sealing members at each sealing station and in which the cover means has a positioning device for bringing the portion of a pack to be sealed, positioned at a sealing station, into engagement with the sealing members of the sealing station to allow sealing to take place.
 9. Apparatus according to claim 8, in which the positioning device includes a member for engaging the pack, an expandable envelope for moving the member toward and away from the sealing members of the sealing station in dependence of the relationship of the pressure in the envelope and the pressure in the sealing station, and a three-way valve, said three-way valve connecting the interior of the envelope with either the atmosphere or the interior of the cover during movement in the first direction. 